Fuel tank purge system and method

ABSTRACT

A fuel tank purge system and method in which fuel vapor stored in a nonvented fuel tank is released and conveyed to a vapor compensated idle system of a carburetor whereby the air-fuel mixture ratio at idle and off-idle will be the same curve whether fuel is coming from the carburetor bowl as liquid fuel or whether a portion of the fuel is coming from the fuel tank as fuel vapor.

United States Patent lnventor Donald D. Stoltman Henrietta, N.Y.

Appl. No. 863,955

Filed Oct. 6, 1969 Patented Oct. 5, 1971 Assignee General MotorsCorporation Detroit, Mich.

FUEL TANK PURGE SYSTEM AND METHOD 9 Claims, 2 Drawing Figs.

US. Cl 123/136, 123/121,123/119 Int. Cl ..F02m21/0 F02m 13/08 Field ofSearch 123/136,

[56] References Cited UNITED STATES PATENTS 2,933,894 4/1960 Johnson etal. 60/3928 3,191,587 6/1965 Hall 123/136 Primary ExaminerMark M. NewmanAssistant Examiner-Cort Flint AttorneysJean L. Carpenter and Arthur N.Krein ABSTRACT: A fuel tank purge system and method in which fuel vaporstored in a nonvented fuel tank is released and conveyed to a vaporcompensated idle system of a carburetor whereby the air-fuel mixtureratio at idle and off-idle will be the same curve whether fuel is comingfrom the carburetor bowl as liquid fuel or whether a portion of the fuelis coming from the fuel tank as fuel vapor.

PATENTED um 519m awed! Q Sak /6121411 ATTORNEY FUEL TANK PURGE SYSTEMAND METHOD This invention relates to a pressure fuel tank purge systemand method for use with engines utilizing fuel such as gasoline and,more particularly, to a system and method for containing andsubsequently consuming hydrocarbon vapor from the fuel tank of aninternal combustion engine. v

It is well known that vapors and gasses emitted from internal combustionengines contribute to the present day problem of air pollution.Accordingly, much attention has been directed to controlling thepolluting emissions from internal combustion engines; Many correctivedevices have been proposed and utilized to control the most obvioussource of emission, that is, of fumes from the engine exhaust andcrankcase. Another source of hydrocarbon emission from an internalcombustion engine is the fuel vapor or hydrocarbons escaping from thefuel system. In particular, gas vapors may escape from the externalvents of both the fuel tank and the carburetor float bowl, either whiledriving or while at rest. It has been estimated that of thisuncontrolled fuel evaporation losses, the loss from the fuel tankaccounts for from 50 percent to approximately 75 percent of this totalloss. In an effort to reduce the hydrocarbon emission from the fuelsystem, various evaporative loss control devices have been proposed andutilized whereby, the fuel vapors are contained and then delivered tothe intake manifold of the engine while in operation for consumptiontherein. This approach has worked successfully to help reduce thehydrocarbon emission directly from the fuel system but, under certainengine operating conditions, this feedback of the hydrocarbon vapors forconsumption in the engine has affected engine operation or has increasedthe exhaust emission of unburned hydrocarbon or both. 1

It is, therefore, the principal object of this invention to improve fueltank purge systems whereby fuel vapor stored in the fuel tank can bepurged from it during engine operation and conveyed to the engine forconsumption therein without affecting the air-fuel ratio of the engineat the particular operating condition at which the fuel vapor isintroduced into the engme.

Another object of this-invention is to provide a vapor purge systemwhich will maintain during engine operation, metering results in thecarburetor which will be the same when handling liquid fuel as whenhandling liquid fuel and fuel vapor.

Another object of this invention is to provide an improved method ofpurging hydrocarbon vapors from a fuel tank whereby the fuel vapor isadmixed with liquid fuel without affecting the air-fuel ratio for theengine at a given operating condition.

Still another object of this invention is to improve a fuel tank purgesystem and method for the purging of fuel vapors whereby this purgingwill not affect engine performance and will not increase exhaustemission.

These and other objects of the invention are obtained by means of a fueltank purge system and method for an internal combustion engine whereinfuel vapor is stored in a nonvented fuel tank which is connected by avalve controlled conduit for the fuel vapor to the idle system of acarburetor, the idle system being calibrated to compensate for theintroduction of fuel vapor so that the mixture ratio at idle andoff-idle will be the same curve whether fuel is coming totally from thecarburetor bowl as liquid fuel or whether a portion of the fuel iscoming from the fuel tank as fuel vapor.

For a better understanding of the invention, as well as other objectsand further features thereof, reference is had to the following detaileddescription of the invention to be read in connection with theaccompanying drawings, wherein:

FIG. 1 is a schematic view of a portion of an engine fue systemincorporating a fuel tank purge system with a carburetor compensatedidle system in accordance with the invention; and

FIG. 2 is a schematic view similar to FIG. 1, but incorporating a secondembodiment of a carburetor compensated idle system.

Referring to the drawings, a conventional'carburetor is indicated at 10and is adapted to be mounted on an engine intake manifold of an internalcombustion engine, not shown, to which the carburetor supplies asuitable fuel-air mixture. Carburetor 10 includes air horn 12, athrottle valve 14, a fuel bowl l6 and well 18, the fuel bowl beingsupplied with fuel from a conduit 20. The quantity of fuel flow to bowl16 is controlled in the normal manner by a float control inlet valve,not shown. A fuel pump 22 supplies fuel to conduit 20 and in turn drawsfuel from a fueltank 26 through a conduit 24.. Fuel reservoir or tank 26is adapted to be filled through a filler pipe 28 normally closed by acap 30 and would normally contain a quantity of liquid fuel 32 with thespace above the fuel level containing fuel vapors 34.

Rather than venting this fuel vapor from the fuel tank to the atmospherethrough a suitable vent, such as a vented fuel tank cap as was done inthe prior art, the cap 30 is a nonvented cap and in order to dischargethe vapor from the tank, the vapor space of the fuel tank 26 isconnected to the idle fuel system of the carburetor 10.

As is well known, the idle system of a conventional carburetor includesan idle tube 40 having an orifice 42 at the lower end thereof positionedin the fuel bowl well with the orifice below the normal fuel level inthe well. The idle tube 40 is connected intermediate its ends viapassage 44 to an idle air-bleed 46 which in turn is in communication viaidle restriction passage 48 with a second or lower idle air-bleed 50 andidle passage 52. Discharge of an air-fuel mixture from the idle passage52 is through adjustable idle mixture needle 54, controlled idle port 56posterior to the throttle valve in the throat of the carburetor whenclosed and through off-idle port 58 anterior thereof.

In the embodiment illustrated in FIG. 1, fuel vapor is delivered intothe idle system through a mctering'orifice 60 into the top of idle tube40 which is connected via conduit 62, pressure regulator 64, conduit 66,valve 68 and conduit 70 to the fuel tank 26. A vacuum relief valve 72and a pressure relief valve 74 are operatively connected to the fueltank, as by conduit 70 to permit breathing and to control the maximumpressure in the fuel tank. Pressure regulator 64 is provided to preventflow in the conduit 66 when the tank pressure is at or below atmosphericpressure. Pressure relief valve 74 is set to open at a pressure withinsafe limits of the fuel tank structure. Valve 68, which can be of anysuitable type, such as an engine oil pressure diaphragm activated valve,is shown herein as a solenoid valve, normally closed, which is connectedby a suitable switch, such as an ignition switch, to a source ofelectrical power, not shown, so that it can be energized upon the startof engine operation.

In operation, the carburetor is calibrated to the optimum air-fuel ratiofor the engine, with the valve 68 closed, in the normal manner. Then,after calibration, the system can be used to purge fuel vapors from thefuel tank when the engine is in operation, at which time valve 68 isopen through the circuit, previously described. Feeding I00 percentvaporized fuel to metering orifice 60 causes the previously calibratedidle tube 40 suction to vary as a direct function of the vapor-flow rateby weight. The increasing flow progressively reduces the idle tube 40liquid delivery to zero at which time the weight of fuel vapors throughthe metering orifice 60 and then to the idle ports 56, 58 will equal theoriginal idle tube liquid calibration. When the fuel vapor pressure inthe fuel tank decreases to atmospheric pressure, the pressure regulatorvalve 64 will close so that the carburetor does not bleed air and hencelean out.

In an actual test, a commercially available 283 CID Chevrolet two-barrelcarburetor manufactured during the 1967 model year by Rochester ProductsDivision of General Motors Corporation was reworked to inject fuelvapors into the top idle bleeds of the carburetor. No changes other theneliminating the top bleeds were made in the carburetor. Airfuel ratiofor various metering orifice sizes, and vapor inlet pressures weredetennined, at idle, by exhaust analysis. Using these particular. sizedmetering orifices, of 0.025-inch restriction, 0.030-inch restriction,0.035-inch restriction and 0.046- inch restriction, the test indicatedthat with tank pressure up to 4 pounds per square inch there was aslight increase in the air-fuel ratio over that previously calibrated,but this was insufficient to affect idle and off-idle operation of theengine and, of course, with this slight increase in the air-fuel ratio,there was a slight decrease in exhaust emission. Thus, with thisarrangement, purging of the fuel tank can be effected through the idlesystem of a carburetor without affecting engine operation or causing anincrease in exhaust emissions.

ln the embodiment of FIG. 2, where like numerals indicate like parts,conduit 62 is connected via metering orifice 60 to the upper end of idlepassage 52 to inject the fuel vapor downstream of the metering area ofthe idle fuel system of the carburetor, but above off-idle port 58. Inthis embodiment, the metering orifice or bleed 60a at the top of idletube 40 is in communication with air horn 12 via conduit 61. Thisarrangement provides the best vapor compensation with the liquid fuelrate decreasing in a linear fashion as the amount of vapor entering theidle system increases.

1 claim:

1. A method of storing and then recovering fuel vapor from the normallynonvented fuel tank of an engine and venting the thus stored fuel vaporthrough the idle system of the carburetor of the engine, said methodcomprising the steps of storing substantially all of the fuel vaporreleased from liquid fuel in the fuel tank under pressure in said fueltank when the engine is not operating, releasing the stored fuel vaporunder pressure during engine operation, conveying the released fuelvapor at above atmospheric pressure to the idle system of the carburetorduring engine operation, admixing the fuel vapor with liquid fuel andaeriform fluid in the idle system of the carburetor to provide apredetermined air-fuel ratio, maintaining this air-fuel ratio bydecreasing the quantity of liquid fuel in direct relation to the amountof fuel vapor conveyed into the idle system of the carburetor, anddischarging the resulting air-fuel mixture from the idle port andoff-idle port of the carburetor.

2. A fuel tank purge system for an internal combustion engine having acarburetor with an idle system including an idle tube connected to anidle air-bleed passage and in communication through an idle restrictionwith a lower idle air-bleed passage and through an idle passage to anidle port and off-idle port of said carburetor, and a pressure fuelreservoir, the systemcomprising valve-controlled conduit means connectedto said pressure fuel reservoir in fuel vapor flow relation thereto and,metering orifice passage means connecting said conduit means to saididle system of said carburetor upstream in terms of the direction offlow of said idle port and said offidle port, said valve-controlledmeans including valve means to block fuel vapor flow to said idle systemwhen the engine is not in operation and a pressure regulator valveadapted to block fuel vapor flow to said idle system when the pressurein said pressure fuel reservoir reaches atmospheric pressure.

3. A fuel tank purge system according to claim'2 wherein said meteringorifice passage means is connected to said idle tube of said idlesystem.

4. A fuel tankpurge system according to claim 2 wherein said meteringorifice passage means is connected to said idle passage of said idlesystem between said idle restriction and said off-idle port.

5. A fuel tank purge system according to claim 2 wherein saidvalve-controlled conduit means includes a pressure relief valve and avacuum relief valve positioned between the pressure fuel reservoir andsaid valve means.

6. A fuel tank purge system for an internal combustion engine having apressure fuel tank and a carburetor with an idle system including anidle tube connected to idle-bleed passages and in communication throughan idle restriction and an idle passage with an idle port and anoff-idle port of said carburetor, said system comprising a vapormetering orifice passage means positioned in communication with the idlesystem of the carburetor upstream of the idle rt and off-idle port ofsaid carburetor, and valve-controlle conduit means, including a pressureregulator valve, and a control-valve,'said valvecontrolled conduit meansbeing connected at one end to the pressure fuel tank in vapor flowrelation thereto and at its other end to said vapor metering orificepassage means, said pressure regulator valve being adapted to block fuelvapor flow to the idle system when the pressure in the pressure fuelreservoir reaches atmospheric pressure, said control valve beingoperable to block the flow of fuel vapor to said idle system of saidcarburetor when the engine is not in operation and operable duringengine operation to permit the flow of fuel vapor to said carburetor.

7. A fuel tank purge system according to claim 6 wherein said vapormetering orifice passage means is connected to said idle tube of saididle system.

8. A fuel tank purge system according to claim 6 wherein said vapormetering orifice passage means is connected to said idle passage of saididle system between said idle restriction and said off-idle port.

9. A fuel tank purge system according to claim 6 wherein saidvalve-controlled conduit means includes a pressure relief valve and avacuum relief valve positioned between the pressure fuel reservoir andsaid valve means.

1. A method of storing and then recovering fuel vapor from the normallynonvented fuel tank of an engine and venting the thus stored fuel vaporthrough the idle system of the carburetor of the engine, said methodcomprising the steps of storing substantially all of the fuel vaporreleased from liquid fuel in the fuel tank under pressure in said fueltank when the engine is not operating, releasing the stored fuel vaporunder pressure during engine operation, conveying the released fuelvapor at above atmospheric pressure to the idle system of the carburetorduring engine operation, admixing the fuel vapor with liquid fuel andaeriform fluid in the idle system of the carburetor to provide apredetermined air-fuel ratio, maintaining this air-fuel ratio bydecreasing the quantity of liquid fuel in direct relation to the amountof fuel vapor conveyed into the idle system of the carburetor, anddischarging the resulting air-fuel mixture from the idle port andoff-idle port of the carburetor.
 2. A fuel tank purge system for aninternal combustion engine having a carburetor with an idle systemincluding an idle tube connected to an idle air-bleed passage and incommunication through an idle restriction with a lower idle air-bleedpassage and through an idle passage to an idle port and off-idle port ofsaid carburetor, and a pressure fuel reservoir, the system comprisingvalve-controlled conduit means connected to said pressure fuel reserVoirin fuel vapor flow relation thereto and, metering orifice passage meansconnecting said conduit means to said idle system of said carburetorupstream in terms of the direction of flow of said idle port and saidoff-idle port, said valve-controlled means including valve means toblock fuel vapor flow to said idle system when the engine is not inoperation and a pressure regulator valve adapted to block fuel vaporflow to said idle system when the pressure in said pressure fuelreservoir reaches atmospheric pressure.
 3. A fuel tank purge systemaccording to claim 2 wherein said metering orifice passage means isconnected to said idle tube of said idle system.
 4. A fuel tank purgesystem according to claim 2 wherein said metering orifice passage meansis connected to said idle passage of said idle system between said idlerestriction and said off-idle port.
 5. A fuel tank purge systemaccording to claim 2 wherein said valve-controlled conduit meansincludes a pressure relief valve and a vacuum relief valve positionedbetween the pressure fuel reservoir and said valve means.
 6. A fuel tankpurge system for an internal combustion engine having a pressure fueltank and a carburetor with an idle system including an idle tubeconnected to idle-bleed passages and in communication through an idlerestriction and an idle passage with an idle port and an off-idle portof said carburetor, said system comprising a vapor metering orificepassage means positioned in communication with the idle system of thecarburetor upstream of the idle port and off-idle port of saidcarburetor, and valve-controlled conduit means, including a pressureregulator valve, and a control valve, said valve-controlled conduitmeans being connected at one end to the pressure fuel tank in vapor flowrelation thereto and at its other end to said vapor metering orificepassage means, said pressure regulator valve being adapted to block fuelvapor flow to the idle system when the pressure in the pressure fuelreservoir reaches atmospheric pressure, said control valve beingoperable to block the flow of fuel vapor to said idle system of saidcarburetor when the engine is not in operation and operable duringengine operation to permit the flow of fuel vapor to said carburetor. 7.A fuel tank purge system according to claim 6 wherein said vapormetering orifice passage means is connected to said idle tube of saididle system.
 8. A fuel tank purge system according to claim 6 whereinsaid vapor metering orifice passage means is connected to said idlepassage of said idle system between said idle restriction and saidoff-idle port.
 9. A fuel tank purge system according to claim 6 whereinsaid valve-controlled conduit means includes a pressure relief valve anda vacuum relief valve positioned between the pressure fuel reservoir andsaid valve means.